When to stop?

So I had a book come out in January, and despite various efforts at promotion, I'm having trouble getting traction with it. The publisher more or less puts the onus on the authors to do the marketing and promotion, which usually isn't a problem for me; I've self-published some stuff that has done fairly well (through my marketing efforts) and thought this would be no different. But the audience for this book has proven harder to reach.

Anyway, I'm not looking for promo ideas so much as asking whether to stop spinning my wheels with this one and move on to the next thing. I have another book coming out soon with another publisher--something much easier to market--but I feel a little like I'm abandoning this baby. And I know it's not like with a movie where if it doesn't find an audience the first weekend it's a goner; the book may yet, later, find readers. I just don't know how much more effort to put into marketing it. Promos are costly and I don't want to throw good money after bad.

Thanks! That's the direction I'm leaning. Just feel a little sad about this book's failure to launch, since I do think it's one of my better works. Guess they can't all be bestsellers.

I think the thing that's really bumming me out is that this one book is the one I worked hardest and longest on, and I had this idea it would be my breakout. Alas, no. Not meant to be. I also had ideas of doing sequels, but now that feels like a waste of time and effort. (Though some would say that sequels can mean getting more readers.) It's such a niche market, this book. I knew that going in, but . . . hope springs infernal.